The present invention relates generally to access control in mobile communication networks and, more particularly, to access control for wireless terminals or machine-type communication (MTC) devices.
The random access channel (RACH) in mobile communication networks provides contention-based access to wireless terminals to request connection setup when no traffic channel has been allocated to the wireless terminal. In systems based on the GSM/EDGE standard, the wireless terminal sends an access request message to the network on the RACH. The access request message includes a randomly generated reference value—such as the Reference Request information—for identification purposes, in lieu of an identifier such as the IMSI, for reasons of security and minimizing the amount of information sent by a wireless terminal to accomplish contention resolution. The wireless terminal then monitors the Access Grant Channel (AGCH) for a response. The network may either accept or deny the access request. If it accepts it, the network transmits an Immediate Assignment (IA) message on the AGCH, identifying the wireless terminal by the random reference value included in the access request message and directing it to a traffic channel. If the network denies access to the requesting wireless terminal, it transmits an Immediate Assignment Reject (IAR) message.
Contention occurs on the RACH occur when two or more wireless terminals attempt to access the communication network at the same time. In the event of a contention, the network will resolve the contention in favor of one of the wireless terminals. The unsuccessful wireless terminals will then “back-off” and make a new access attempt at a later time. As the number wireless terminals increases, there is a greater probability of contention between the wireless terminals and a greater number of access attempts will fail. If too many contentions occur, throughput on the RACH will be significantly reduced.
The anticipated introduction of a large volume of machine-type communication (MTC) devices in the near future will greatly increase the problem of congestion on the RACH. MTC devices are devices, such as a meter or sensor, that collect and send data to an MTC server or other MTC device over a communication network. It is expected that MTC devices will far outnumber non-MTC devices, such as user terminals for voice and data communications by human users. Therefore, there is a need to implement new procedures to control network access by MTC devices and minimize the impact on non-MTC devices.